MaTISSE (Mammographic and Tomographic Imaging with Synchrotron ligh Source at Elettra) is a project aiming to develop a digital detector for breast tomography with synchrotron radiation to be used at the SYRMEP beam line at Elettra Synchrotron Light Source in Trieste (Italy).
Tomography is a very outstanding technique in the breast imaging field since it allows to reconstruct the inner structure of the breast by acquiring projections of the organ at different angles and then elaborating the data. This is very important in the diagnosis of breast tumors since it helps to discriminate the shape of the lesions.
Unluckily this technique requires a very high number of projections in order to reach a high spatial resolution at this is not practicable with conventional x-ray tubes because a very high dose of radiation would be given to the patient. The beam divergence of an x-ray tube is also a problem in the image reconstruction phase.
The use of a synchrotron radiation monochromatic beam allows to acquire tomographic images with a low dose and without the problems given by the beam divergence. A digital detector is mandatory when applying the tomographic technique because the data must be elaborated in order to reconstruct the image. The main detector requirements are:
- High efficiency in order to keep the dose to the patient low enough.
- High resolution in order to see details as small as a few hundred microns, like microcalcifications.
- High dynamic range in order to see both high and low contrast details (for example calcifications and nodules).
- Complete discrimination of the signal given by the photons from the noise in order to obtain a high image quality.
- High speed in order to keep the total examination time short enough.
MATISSE is based on a silicon microstrip detector array with application specific read out electronics working in single photon counting mode.
The detector is oriented with the strips parallel to the impinging beam in order to achieve almost 100% absorption efficiency and good spatial resolution given by the strip pitch (100 µm) times the detector height (300 µm). The use of the single photon counting technique allows the complete discrimination of the signal from the noise and a dynamic range of about 105. The final system should be made of 4 detectors aligned in order to cover an area of the beam of 200x0.6 mm2.